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Fish is rich in beneficial omega-3 fatty acids, though while cooking under high temperatures we may destroy any benefit of fish. But different cooking methods affect fish differently. Surprisingly, I read that frying reduces amount of heavy metals better than any other cooking method. Is it true? If so, should we opt for fried fish or still it is better to avoid it as any other fried food?

The evidence that omega-3 fatty acids (FAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have a cardioprotective effect is increasing, and the American Heart Association recommend consuming at least two servings of fish per week.[1] [2] These cardioprotective benefits can be obtained by eating either farmed and wild fish, with the highest amounts of omega-3 being found in oily fish such as salmon or mackerel. They have been observed from as little as one fish meal per week and improve with every extra meal consumed up to five fish meals per week.[3] One study showed a 29% decrease in mortality in the two year period following a heart attack in patients who were advised to eat oily fish compared to those who were not.[1] In another, where over 18,000 patients with high cholesterol were observed over a five year period, those who were prescribed 1800 mg/day of EPA in addition to statins had significantly fewer coronary events than those prescribed just statins.[4]
Studies have also shown that the mineral and FA content of fish are significantly affected by different cooking methods.[5] [6] One study, for example, concluded that thermal processing of tuna damages the beneficial fats contained within it.[7] In another study, a comparison of cooking methods (baking, frying and microwaving) used to prepare seabass showed that the protein content was significantly changed by all cooking methods and FA levels were generally decreased by most methods.[6] Omega-6 FA levels were shown to increase with frying and omega-3 FA levels increased with microwaving.[6] The conclusion was that to gain the optimum health benefits of FAs from fish, it should be broiled, baked or microwaved, which result in lower levels of less favourable FAs.[5] [6] [8] However, other studies have found that different cooking methods have no effect on omega-3 FA levels. Although in one study fried fish had increased levels of omega-6 FAs and monounsaturated FAs, these were attributed to the oil used for frying.[8]
In addition to effects on FA content, cooking practices can also affect the levels of pollutants, such as heavy metals, present in fish. One study on hammour fish found that, although the majority of the heavy metals present were below maximum permitted levels (MPLs), the levels of lead and arsenic exceeded them.[9] Cooking methods had variable effects on pollutant levels; lead levels decreased with all cooking methods (-16.2% with roasting, -20.7% with frying and -13.2% with broiling), whilst the results for cadmium varied (no change with roasting, totally eliminated with frying and -20.7% with broiling).[9] Freezing the raw fish for six months had no significant effect.[9] Other investigations have found that various cooking methods can affect both the nutrient composition and levels of heavy metal pollutants.[10] The researchers of this study concluded that both excessive frying and the use of salt should be avoided in order to maximise the health benefits of the fish. Furthermore, in order to minimise heavy metal exposure and maximise nutritional benefit, a variety of fish species should be consumed.[10] With regards to mercury levels,a general decrease has been seen with a variety of cooking methods while some mercury can leach out into the water when the fish were boiled.[11]
Baking, boiling and frying fish have been shown to reduce endocrine-disrupting perﬂuorinated compounds (PFCs), for example, baking at 160oC for 15 minutes has been shown to completely remove PFCs.[12] Where radio-caesium was tested, levels appeared increased after deep frying in a study of fish caught on the Savannah River, however this was attributed to the loss of weight from the fish during cooking (i.e.increases in concentration).[13]
In addition to a potential loss of nutrients and alterations in pollutant levels, cancer-promoting substances found in cooked fish are another cause for concern. Carcinogenic heterocyclic amines (HCAs) are produced during various cooking processes. The quantity of HCAs ordinarily consumed is thought to be too low to specifically cause cancer, however, in combination with other mutagens or carcinogens they can be tumour promoters. Hence, it is advisable to minimise HCAs in the diet, for example by microwaving fish instead of frying. It has also been established that supplementing the diet with soy-isoflavones suppresses breast cancer induction by HCAs.[14] Nitrosamines, another group of carcinogenic compounds are also formed during the cooking of fish.[15] This potential for the generation of carcinogenic compounds during cooking is supported by an observed direct association between white fish cooked at high temperatures (pan frying, oven broiling and grilling) and prostate cancer.[16]
However, despite these potential risks, it appears that the health benefits of omega-3 FAs and other nutrients obtained by eating fish may outweigh any associated dangers of cooking FAs rich food. However, care should be taken with the cooking method, temperature, and time. Overall baking and boiling appear to be the safest fish cooking ways. Consuming a variety of species can also decrease the risk of exposure to excessive levels of heavy metals and other pollutants while maximising nutritional benefit.
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[2] Kris-Etherton PM, et al. (2002) Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Circulation, 106, 2747–2757
[3] Psota TL, et al. (2006) Dietary omega-3 fatty acid intake and cardiovascular risk. Am J Cardiol, 98, 3–18
[4] Yokoyama M, et al. (2007) Japan EPA lipid intervention study (JELIS) Investigators. Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis. Lancet, 369, 1090–1098
[5] Gokoglu N, et al. (2004) Effects of cooking methods on the proximate composition and mineral contents of rainbow trout. Food Chem, 84(1), 19-22
[6] Türkkan AU, et al. (2008) Effects of cooking methods on the proximate composition and fatty acid composition of seabass (Dicentrarchus labrax, Linnaeus, 1758). Food and Bioproducts Processing, 86(3), 163-66
[7] Aubourg S, et al. (1995) A comparison between conventional and fluorescence detection methods of cooking-induced damage to tuna fish lipids. European Food Res Technol, 200(4), 252-55
[8] Neff MR, et al. (2014) Effects of different cooking methods on fatty acid profiles in four freshwater fishes from the Laurentian Great Lakes region. Food Chem, 164, 544-50
[9] Ganbi, HHA. (2010) Heavy metals pollution level in marine hammour fish and the effect of popular cooking methods and freezing process on these pollutants. World J Dairy Food Sci, 5(2), 119-126 [10] Musaiger AO & D’Souza R. (2008) The effects of different methods of cooking on proximate, mineral and heavy metal composition of fish and shrimps consumed in the Arabian Gulf. Arch Latinoam Nutr, 58(1), 103-9
[11] Miero CL, et al. (2016) Fish and mercury: influence of fish fillet culinary practices on human risk. Food Control, 60, 575-81
[12] del Gobbo L, et al. (2008) Cooking decreases observed perfluorinated compound concentrations in fish. J Agric Food Chem, 55(16), 7551-9
[13] Burger J, et al. (2004) Effects of cooking on radiocesium in fish from the Savannah River: exposure differences for the public. Faculty Research & Creative Activity. Paper 60.
[14] Sugimara T, et al. (2004) Heterocyclic amines: mutagens/carcinogens produced during cooking of meat and fish. Cancer Sci, 95(4), 290-99
[15] Huang DP, et al. (1981) Volatile nitrosamines in salt-preserved fish before and after cooking. Food and Cosmetics Toxicology, 19, 167-71
[16] Joshi AD, et al. (2012) Fish intake, cooking practices, and risk of prostate cancer: results from a multi-ethnic case-control study. Cancer Causes Contr, 23(3), 405-20